Many of us are unable to guide ourselves without oursmartphone, but sharks only use their own instincts to navigate their way through the vastness of the ocean. As they do? Using his interpretation with the earth magnetic field, in the same way as turtles or seabirds. A team of biologists from Florida State University has just demonstrated this hypothesis in a study recently published in the specialized journal Current biology.
Sharks use the magnetic field as a compass and map to navigate the middle of the ocean
long migrations
In 2005, a team of researchers tracked a great white shark that had traveled from South Africa to Australia in a straight line and returned following the same path. Scientists have suspected since the 1970s that elasmobranchs – a subclass of cartilaginous fish that includes sharks, rays and sawfish – are able to detect magnetic fields.
Many species travel long distances, as their habitat can cover thousands of kilometres. Some, like the white shark mentioned above, have also shown great loyalty when it comes to returning to a certain point.. It would be like they had a compass and a map to guide them through the middle of the ocean. However, to date no one had shown that sharks use these recordings of the magnetic field to move.
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To solve the mystery, a team of researchers led by Florida State University ecologist Bryan Keller decided to mimic the habitat of these sharks in an artificial environment. Specific, Forraron a cage the size of a small chamber with copper wire and placed a small basin in the center. By running an electric current through the wiring, they were able to generate a custom magnetic field in the center of the pool. The team then collected 20 specimens juvenile shovel sharks – a species known to migrate hundreds of kilometers – captured off Florida. They were placed in a pool, one at a time, and lthey allow you to swim freely under three different magnetic fields, applied in random succession. One field mimicked the natural field on Earth where the sharks were collected, while the others mimicked fields 600 kilometers north and 600 kilometers south of their range.
Representation of the Earth’s magnetic field
Photo: Florida State University
When the applied magnetic field was the same as where they were collected, the researchers found that the animals swam in random directions. But when the signal corresponding to a southern latitude was applied to them, the Sharkss changed direction repeatedly to swim north, which they interpreted as the way back. In these cases, they were anchored to one of the walls of the pool, from which they seemed to want to come out. This fact has led to the hypothesis that they are able to use these magnetic fields for their long distance migrations.
But that was not all. Scientists found that the sharks weren’t going in any direction when they swam under the signal from the magnetic field further north. One possible explanation, experts say, is that this species does not typically migrate to more northern latitudes, so it is rarely forced to find its way back south. This fact could reinforce the idea that we are in front of a learned behavior: they would not know what to do in the north, because they would never have been there beforea hypothesis, however, that has yet to be proven.
Learned behavior possible
“Experience does not allow us to conclude whether or not they behave instinctively or whether it is a learned ability,” comments Keller himself. National Geographic Spain by email. In other work with salmon and sea turtles, we were able to determine that the magnetic navigation responses were instinctive (the animals analyzed had no “external experience” with which they could learn what to do). In other researchers’ studies of birds, it appears that magnetic navigation responses are learned: adults orient themselves magnetically, but inexperienced youngsters do not. It is not yet known whether sharks are more like birds or more like sea turtles and salmon.”
test pool
Data collected on the behavior of sharks in response to magnetic stimuli. The red circles indicate the position of the shark’s head at different times during the test.
Photo: © Bryan Keller
Although the researchers used shovel sharks to conduct their experiments, Keller thinks eitherOther species, such as the great white shark, used to undertake long migrations, could also have this ability. With the main question answered, researchers must now find out how they do it.
Genetic divergence and magnetism
“East is probably the most exciting part of the investigation -said the expert. We examined the genetics of different groups of sharks in coastal areas of the northwest Atlantic Ocean. What we discovered is thatthat magnetic differences between geographic locations coincided with the genetic divergence of populations. We found evidence of this in both nuclear DNA (inherited from both parents) and mitochondrial DNA (inherited only from the mother), particularly the latter,” he says. This discovery means, according to Keller, that female sharks that return to the vicinity of their birthplace to breed most likely use magnetic signals to determine where their birthplace is, clear biogeographic evidence that sharks use magnetic signals. magnetic to navigate.
Do they use the magnetite contained in some of their cells? Or a photoreceptor protein in your retina? The answers to these questions will be described in another chapter of the fascinating world of sharks.